Abstract: In a phase monitoring arrangement for a three phase network which supplies a controlled d.c. motor through a controlled converter, a power line dependent discriminator along with R-C circuits forms a smoothed, rectified monitoring voltage which depends on the phase sequence and is sensitive thereto and to phase failure along with a supplementary monitoring voltage dependent only on phase failure, the rectified monitoring voltage and supplementary monitoring voltage being supplied to an evaluating circuit comprising differential comparing amplifiers at which the monitoring voltages are compared with constant reference voltages independent of faults and the output thereof used to control switching means and a current regulator so that in the event of incorrect phase sequence or of a phase failure, the switching means feed a blocking signal which suppresses firing pulses to the controlled converter and the current regulator feeds a control signal to control the converter to its operating limit.